Processes for the treatment of acid gas streams containing hydrogen sulfide to produce sulfur are well known, with the best-known process possibly being the Claus process. In the Claus process, the acid gas stream is partially oxidized by the use of an oxygen-containing stream, such as oxygen, air or oxygen-enriched air, at a temperature sufficiently high to combust a portion of the hydrogen sulfide (H2S) to sulfur dioxide (SO2) and to combust any hydrocarbons or other combustible compounds in the acid gas stream. Typically the combustion flame temperature is maintained in a range of about 1500 to about 2000° F. The combustion is regulated to produce a product gas stream, which desirably has a hydrogen sulfide to sulfur dioxide ratio of about 2:1. This ratio is the stoichiometric relationship between hydrogen sulfide and sulfur dioxide when they are reacted to produce sulfur and water.
The Claus process reactions can be considered to be:2H2S+3O2→2SO2+2H2O  (1)SO2+2H2S→3S+2H2O  (2)
By review of these reactions, it will be observed that hydrogen sulfide can be combusted readily to produce sulfur dioxide. When the ratio of the hydrogen sulfide and sulfur dioxide is adjusted to the proper range, the reaction shown in equation (2) can be used to produce sulfur. While it is difficult to achieve complete reaction in any such system, the Claus process is very effective since it uses catalytic steps downstream from the combustion zone to convert the reactant gases to sulfur.
In many instances there will be some carbon dioxide in the acid gas stream initially and the total composition of the acid gas stream must be taken into account when the amount of oxygen to be charged to the combustion zone is determined.
The reaction gases are typically cooled to a temperature generally in the range of about 500 to about 600° F. or cooler to separate sulfur from the gaseous mixture produced in the combustion zone. The sulfur is recovered as a liquid and the reaction product gases are passed to Claus process catalytic reaction units. One or more Claus unit catalytic chambers may be used with subsequent cooling of the reaction gases and sulfur condensation after each unit. Such processes are very well known to those skilled in the art and need not be discussed in detail.
The energy recovered from such processes is primarily that produced as a result of the oxidation in the combustion zone, plus the heat produced in the catalytic reaction zones of the Claus unit. This heat recovery is offset to a certain extent by the necessity to heat the reaction mixtures after each sulfur separation step to a suitable temperature for charging to the next catalytic Claus reaction zone. Accordingly, only limited amounts of energy are produced for export to other processes by the conversion of the acid gas stream.
It is further well known that tail gases discharged from the Claus reaction may contain minor quantities of hydrogen sulfide, sulfur dioxide, as well as other light gases in some instances. Such gases are desirably processed before discharge to the atmosphere, as well known to those skilled in the art.
Since this process involves relatively high temperature equipment, it would be advantageous if the process were used to produce additional energy as well as conversion of the hydrogen sulfide gas in the acid gas stream.